Hereinbefore and hereinafter the terms alkyl ammonium thiocyanate and alkyl amine encompass alkylene diammonium dithiocyanates and alkylene diamines respectively as well as their monothiocyanate and monoamine counterparts.
In the lubricating oil field such as in the area of gear oils, transmission fluids, marine oils and, particularly, in gas turbine engine oils, extensive efforts are being made to develop lubricating oil compositions of ever-increasing load-carrying ability without sacrificing wear, corrosion resistance and oxidation resistance. One class of materials found to impart improved load-carrying properties, that is, extreme pressure (EP) properties to lubricating oil compositions without detrimentally affecting other properties are the hydrocarbyl amine salts of thiocyanic acid. These salts and their use in lubricating compositions as load-carrying improvement additives are described in U.S. Pat. No. 3,330,763. Although the amine thiocyanates described therein are effective EP improving agents, there is a continuing search due to the high load demands on modern day lubricant oils to further improve the effectiveness of these salts. One means would be to utilize the amine thiocyanate in conjunction with a second additive substance which would result in a synergistic enhancement of the load-carrying properties of the thiocyanate salt as described in coassigned copending applications, Ser. No. 160,192, filed July 6, 1971 now U.S. Pat. No. 3,756,952 and Ser. No. 190,310, filed Oct. 18, 1971, now U.S. Pat. No. 3,767,573. However, in view of the fact the high additive contents in lubricating oils are today reaching a point which is adversely affecting the lubricating properties of the oils and the more additive materials and quantities introduced into the lubricant oils the greater the cost, there is a need for an alternative means of enhancing the load-carrying properties of the alkyl ammonium thiocyanate additive per unit additive weight.